Lock structures, particularly in relation to high-security locks, have the tendency to involve increasingly complex mechanisms in order to achieve higher levels of security. A natural consequence of such complexity is that lock mechanisms involve more moving parts to achieve more combinations. In order to re-key a lock, whereby the combination of the lock is changed, it is necessary to disassemble the lock, adjust or replace the necessary components of the lock and then reassemble the lock. This process is very involved and time consuming, and requires the skills of a professional locksmith.
The robustness of locks is another consideration when providing locks in which the combination is to be changed regularly. This is often the case with high-security locks. Lock manufacturers have produced locks for this purpose in which only part of the lock structure is required to be removed and re-keyed in order to provide new combinations. Typically, it is the lock plug which is removed, re-keyed and then replaced. However, re-keying the lock plug still requires disassembly and reassembly of the lock plug and is still very much an involved and time consuming process. The procedure for removing and replacing such lock plugs is not simple. The lock must be designed so that the processes of removing and replacing the lock plug are relatively quick and efficient. The lock structure which is not to be removed and the removable part must both be able to withstand the removal and replacement procedures; any damage caused thereto could result in the entire lock having to be replaced. Care must be taken in ensuring that the removable part is correctly aligned so that it is in proper working engagement with the rest of the lock structure. This is not a trivial exercise and requires a high degree of precision. Regular changing of lock combinations can, therefore, add up to a costly and troublesome exercise. It has become desirable in the high-security lock industry to be able to offer master keying. Master keying involves a hierarchy of keys. The number of locks a key can open depends upon how high up the hierarchy the key is positioned. Typically the hierarchy consists of standard keys opening unique locks, master keys opening a number of locks, and a grandmaster key opening all or nearly all locks.
In a paper by Mr Matt Blaze, ‘Cryptology and Physical Security: Rights Amplification in Master-Keyed Mechanical Locks’, IEEE Security and Privacy (March/April 2003), the inherent problems associated with master keying were discussed. In summary, master keying actually reduces the number of possible combinations that can be applied to a lock. This reduces the security that such locks can offer. Where master keying has been implemented by profiling it has been noted that this may also reduce the strength of the key leading to operational difficulties.
Accordingly, it is an object of the present invention to provide a lock structure which offers a reasonable level of security and robustness.
It is a further preferred object of the present invention for such a lock to facilitate changing combinations in which a minimum number of moving parts are required to be replaced. The process for changing combinations is intended to be relatively simple in comparison with other locks.
It is a further object of the present invention to provide keys adapted for use with the inventive lock.
It is a further preferred object of the present invention to provide a lock which offers improved master keying potential, in which master keying does not substantially reduce the number of operational combinations which are available.